JP4543372B2 - Thread cutting method for steel pipe - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method of thread cutting using a chaser at a pipe end or the like of a steel pipe, and more particularly to a screw cutting method capable of improving the service life of a blade portion of a chaser.

  Conventionally, for example, as a method of efficiently threading steel pipes for oil well pipes, etc., using a chaser in which a plurality of thread-shaped blade parts are arranged in a straight line, the arrangement direction of the blade parts of the chase is changed to the axis of the steel pipe A method is known in which a steel pipe is sequentially cut by each blade portion by positioning it parallel to the direction and then feeding it in the axial direction while rotating the steel pipe. More specifically, when performing thread cutting using the above-described chaser, the cutting amount per one time (one pass) (steel pipe before cutting) in order to suppress the cutting load and avoid chipping of the blade portion, etc. The distance between the outer surface of the blade and the cutting edge of the blade part during cutting is regulated, and the positional relationship between the blade part and the steel pipe to be cut is adjusted, and the cutting of the same part of the steel pipe is repeated over several passes. The final screw shape is formed.

  By the way, in recent years, the development of oil wells is carried out even under severe conditions, so demand for difficult-to-cut materials such as high Cr-containing steel with excellent corrosion resistance as materials for oil well pipes has increased. There is a problem that the life of the steel pipe is reduced due to the chipping of the part and the productivity of the steel pipe subjected to thread cutting is lowered.

  Accordingly, various proposals have been made that specialize in the material and shape of the chaser in order to improve the life of the chaser (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5). .

  However, the conventional techniques described in Patent Documents 1 to 5 are merely to propose a material and a shape of a chaser for the purpose of improving the life, and various types of workpieces are cut when performing screw cutting using the chaser. It does not teach any specific cutting method useful in actual operation, such as how to set the cutting area per pass in accordance with the material of the steel pipe.

In addition, since various types of steel pipes to be cut are suitable for steel pipes to be cut, such as high Cr content steels that are the most difficult to cut, the Chezers, which are specialized in materials and shapes, are generally expensive. When all the steel pipes to be cut, including carbon steel, which is relatively easy to cut using a chaser, are thread-cut, there is a problem that the cost increases.
JP 60-172403 A JP 60-197317 A JP-A-5-277809 JP-A-11-207524 Japanese Patent Laid-Open No. 11-320255

  The present invention has been made to solve such problems of the prior art, and in order to improve the life of the blade, it is not necessary to dare to use a special chaser as proposed in the prior art. It is an object of the present invention to provide a method for thread cutting of a steel pipe that gives useful guidelines in actual operation.

  In order to solve the above-mentioned problems, the inventors of the present invention have intensively studied various cutting conditions using an existing chaser. As a result, in order to improve the life of the blade portion of the chaser, the average cutting of the blade portion constituting the chaser It has been found that a certain relationship needs to be established among the area, the height of the blade for finishing cutting, the width of the blade for finishing cutting, the cutting speed, and the Cr content of the steel pipe to be cut.

  More specifically, first, if the width of the cutting edge for finishing cutting is narrow (or if the height of the cutting edge for finishing cutting is high), the cutting edge generated by cutting will be applied to the cutting edge. As a result of the increase in the thickness of the chips that are touched and dragged in the cutting direction, the cutting resistance tends to increase.To improve the life of the blade, if the width of the blade for finishing cutting is narrow (or If the height of the blade for finishing cutting is high), it was considered that the average cutting area of the blade needs to be set small accordingly. Next, if the cutting speed is increased, the amount of heat generated by the cutting increases. As a result, heat welding between the steel pipe material and the blade portion is likely to occur. Therefore, in order to improve the life of the blade portion, the cutting speed is increased. In this case, it was considered necessary to set the average cutting area of the blade portion to be small accordingly. Furthermore, when the Cr content of the steel pipe to be cut increases, work hardening increases and thermal conductivity decreases, resulting in increased cutting resistance and thermal welding. When cutting a steel pipe to be cut with a large Cr content, it was considered necessary to set the average cutting area of the blade portion small.

  In other words, in determining the upper limit of the average cutting area of the blade that can improve the life of the blade (maintain a predetermined life), the height of the blade for finishing cutting, the blade for finishing cutting Based on the idea that the width of the part, cutting speed and Cr content of the steel pipe to be cut will have a great influence, the relationship between these parameters and the average cutting area of the blade that can improve the life of the blade As a result of quantitative examination, it has been found that the life of the blade can be improved if a certain relationship is established. The present invention has been completed based on the knowledge found by the inventors of the present invention.

That is, the present invention is a method of threading a steel pipe using a chaser provided with a plurality of blades for cutting a screw, wherein the average cutting area of the blades is S (mm ² ), and for finishing cutting. When the width of the blade is B (mm), the height of the blade for finishing cutting is H (mm), the cutting speed is V (m / min), and the Cr content of the steel pipe to be cut is C (%), The present invention provides a thread cutting method for a steel pipe, characterized in that cutting is performed under conditions that satisfy the following expression (1).
S ≦ 5.68 × 10 ⁻¹ × B-6.76 × 10 ⁻² × H−1.12 × 10 ⁻⁵ × V ² −1.68 × 10 ⁻² × C-5.82 × 10 ⁻¹ ... (1)

  Here, the average cutting area S of the blade part in the formula (1) is the total cutting area of the blade part viewed from the cutting direction (corresponding to the direction orthogonal to the axial direction of the steel pipe to be cut) It means a value divided by the product of the number, and can be controlled by appropriately setting the cutting depth of the blade (the distance between the outer surface of the steel pipe before cutting and the cutting edge of the blade during cutting). . The finishing cutting blade portion is a blade portion (the blade portion located on the most downstream side in the feed direction of the steel pipe) to be used for the last cutting among the plurality of blade portions constituting the chaser, and the formula (1) The height H of the cutting edge for finishing cutting in this means the length in the cutting direction (direction perpendicular to the cutting direction) of the cutting edge for cutting viewed from the cutting direction, and the width B of the cutting edge for finishing cutting Means the width (length along the axial direction of the steel pipe to be cut) at the center in the height direction of the blade for finishing cutting as viewed from the cutting direction. Further, the cutting speed V corresponds to the peripheral speed of the steel pipe to be cut.

  According to the present invention, the cutting speed V is set on the basis of production efficiency and the like, and the set cutting speed V is determined based on the height H of the finishing cutting blade portion in the existing Chesser used for cutting, the finishing cutting blade portion. By substituting into the formula (1) together with the width B and the Cr content C of the steel pipe to be cut, the upper limit value of the average cutting area S of the blade portion that can improve the life of the blade portion of the chaser (can maintain a predetermined life) Will be determined. When the steel pipe is thread-cut, the cutting amount of the blade portion may be set so that the average cutting area S does not exceed the determined upper limit value, and an extremely useful guideline can be obtained in actual operation.

  In addition, when cutting with the first cutting blade portion among the blade portions constituting the chaser, the cutting resistance is large because the black skin (scale) generated on the surface of the steel pipe to be cut is cut. The cutting edge corner may be chipped and the life may be shortened.

  The inventors of the present invention have made extensive studies to solve the above problems, and as a result, in order to suppress chipping of the cutting edge corner portion of the first cutting blade portion, the cutting edge corner portion has an appropriate curvature radius (of the corner portion). It has been found that it is effective to chamfer so that the stress concentration is relaxed and the radius of curvature does not deteriorate the cutting function.

That is, when the radius of curvature of the cutting edge corner portion of the first cutting blade portion viewed from the cutting direction among the plurality of blade portions provided in the chaser is r (mm), the following formula (2) is satisfied. Cutting with a chaser is preferred.
0.2 × B ≦ r ≦ 0.5 × B (2)

  Here, the first cutting blade portion means a blade portion (blade portion located on the most upstream side in the feed direction of the steel pipe) used for the first cutting among a plurality of blade portions constituting the chaser.

  According to such a configuration, by setting r ≦ 0.5 × B, the stress concentration at the corner portion is reduced by 0.2 × B ≦ r without lowering the cutting function at the first cutting blade portion. Can be mitigated, and chipping at the corner of the blade edge can be suppressed to further improve the service life.

  According to the steel pipe thread cutting method of the present invention, the cutting speed V is set based on the production efficiency and the like, and the set cutting speed V is used as the height H of the cutting edge for finishing cutting in the existing Chesser used for cutting. By substituting into the formula (1) together with the width B of the finish cutting blade portion and the Cr content of the steel pipe to be cut, the average of the blade portions can improve the life of the blade portion of the chaser (maintain a predetermined life). The upper limit value of the cutting area S is determined. When the steel pipe is thread-cut, the cutting amount of the blade portion may be set so that the average cutting area S does not exceed the determined upper limit value, and an extremely useful guideline can be obtained in actual operation.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view showing a state where a thread cutting method according to an embodiment of the present invention is applied. As shown in FIG. 1, the method according to the present embodiment is a method in which a steel pipe P is thread-cut using a chaser CH provided with a plurality (two in the present embodiment) of blade portions C1 and C2. When cutting, first, the arrangement direction of the blade portions C1 and C2 of the chaser CH is positioned parallel to the axial direction of the steel pipe P (the left-right direction on the paper surface of FIG. 1). And the outer surface of the steel pipe P is cut in order by each blade part C1 and C2 by sending to the axial direction (direction of the arrow shown in FIG. 1), rotating the steel pipe P. As shown in FIG.

  More specifically, when performing thread cutting using the chaser CH, the cutting amount per one time (one pass) (cutting) in order to suppress the cutting load and avoid the chipping of the blade portions C1, C2, etc. The distance d) between the outer surface of the previous steel pipe P and the cutting edge of the blade part being cut is regulated, and the positional relationship between the blade parts C1, C2 and the steel pipe P (the vertical positional relationship of the paper surface in FIG. 1). By adjusting (moving the positions of the blade portions C1 and C2 upward in the drawing in FIG. 1 from the previous pass), by repeatedly cutting the same portion of the steel pipe P over several passes, the final screw A shape is formed.

Here, in the cutting method according to the present embodiment, the average cutting area of the blade portions C1 and C2 is S (mm ² ), the width of the finishing cutting blade portion is B (mm), and the height of the finishing cutting blade portion is the height. When H (mm), the cutting speed is V (m / min), and the Cr content of the steel pipe to be cut is C (%), cutting is performed under conditions that satisfy the following expression (1).
In other words, the cutting is performed with the average cutting area S with the upper limit of the value calculated on the right side of the formula (1).
S ≦ 5.68 × 10 ⁻¹ × B-6.76 × 10 ⁻² × H−1.12 × 10 ⁻⁵ × V ² −1.68 × 10 ⁻² × C-5.82 × 10 ⁻¹ ... (1)

  Here, the average cutting area S of the blade portions C1 and C2 in the expression (1) is a blade viewed from the cutting direction (a direction perpendicular to the axial direction of the steel pipe P and perpendicular to the paper surface of FIG. 1). It means a value obtained by dividing the total cutting area of the parts C1 and C2 by the product of the number of passes and the number of blade parts (two in this embodiment). More specifically, for each pass, the area of the region S1 (hatched region) to be cut by the blade C1 and the region S2 to be cut by the blade C2 (the region S2 is not cut by the blade C1). It means a value obtained by adding the area of the region cut only by the blade C2) and dividing the sum of all the added areas in all passes (total cutting area) by the product of the number of passes and the number of blades. . The finishing cutting blade portion is a blade portion C2 (blade portion located on the most downstream side in the feed direction of the steel pipe P) used for the last cutting among the plurality of blade portions C1 and C2 constituting the chaser CH. Yes, the height H of the finishing cutting blade C2 in the expression (1) is the cutting direction of the finishing cutting blade C2 as viewed from the cutting direction (the direction perpendicular to the cutting direction, and the top and bottom of the paper surface of FIG. The width B of the finish cutting blade C2 is the width at the center in the height direction of the finish cutting blade C2 as viewed from the cutting direction (along the axial direction of the steel pipe P). Length). Further, the cutting speed V corresponds to the peripheral speed of the steel pipe P.

Each parameter B on the right-hand side of Equation (1), ^H, the coefficients of ^V 2, C, the material is carbon steel (Cr content 0 to 2%, Ni content of less 0.5%), 13Cr steel (Cr Each steel pipe P composed of 9 to 18% content, Ni content 0.5% or less) and high alloy steel (high alloy) (Cr content 20% or more) is subjected to a cutting test under various conditions, approximating blade portion C1, the case C2 life was sufficient actual values of S in (if a lower limit value of the acceptable life), B, H, a V ² and C by the regression equation with the parameters of ( (Approximation by least square method). FIG. 2 is a graph showing the result of approximating the actual value of S with a regression equation calculated on the right side of Equation (1), where the horizontal axis is the actual value of S and the vertical axis is the right side of Equation (1). Each calculated value is shown. As shown in FIG. 2, both of them show a very good correlation, and it is appropriate to select B, H, V ² , and C as parameters for determining the upper limit value of S. The result is shown.

  According to the cutting method according to the present embodiment, the cutting speed V is set based on the production efficiency and the like, and the set cutting speed V is set to the height H of the finishing cutting blade C2 in the chaser CH, the finishing cutting blade. By substituting into the formula (1) together with the width B of the part C2 and the Cr content C of the steel pipe P, the blade part C1, which can improve the life of the blade parts C1, C2 of the chaser CH (can maintain a predetermined life), The upper limit value of the average cutting area S of C2 is determined. Therefore, when the steel pipe P is thread-cut, the cutting amount d of the blade portions C1 and C2 may be set so that the average cutting area S does not exceed the determined upper limit value.

In the present embodiment, as a preferable aspect, the curvature radius of the edge corner portions C11 and C12 of the first cutting blade portion C1 viewed from the cutting direction among the plurality of blade portions C1 and C2 provided in the chaser CH is set. In the case of r (mm), the following formula (2) is satisfied.
0.2 × B ≦ r ≦ 0.5 × B (2)

  Here, the first cutting blade portion C1 is the blade portion (the blade portion located on the most upstream side in the feed direction of the steel pipe P) used for the first cutting among the plurality of blade portions C1 and C2 constituting the chaser CH. ).

  With such a configuration, the stress concentration at the corners C11 and C12 can be relaxed without reducing the cutting function at the first cutting blade C1, and the chipping at the corners C11 and C12 can be suppressed. The lifetime can be further improved.

  Hereinafter, the features of the present invention will be further clarified by showing examples.

ここで、表１に示す評価結果は、被切削鋼管が炭素鋼からなる場合には、７０（±１０％）本の被切削鋼管を刃部の欠損等が生じることなく切削可能であったときを「○」とし、それより多くの本数を切削可能であったときを「◎」、それより少ない本数しか切削できなかったときを「×」とした。同様にして、被切削鋼管が１３Cｒ鋼からなる場合には、５０（±１０％）本の被切削鋼管を刃部の欠損等が生じることなく切削可能であったときを「○」とし、それより多くの本数を切削可能であったときを「◎」、それより少ない本数しか切削できなかったときを「×」とした。また、被切削鋼管がハイアロイからなる場合には、３０（±１０％）本の被切削鋼管を刃部の欠損等が生じることなく切削可能であったときを「○」とし、それより多くの本数を切削可能であったときを「◎」、それより少ない本数しか切削できなかったときを「×」とした。 Screw cutting was performed under the conditions of the chaser and the steel pipe to be cut shown in Table 1, and the life of the chaser was evaluated. For carbon steel and 13Cr steel, K153R3 (corresponding to base material hardness P30) manufactured by Sumitomo Electric Industries, Ltd. is used as a thread cutting chaser so that the corner of the first cutting blade has a predetermined radius of curvature. Chamfered. As for the high alloy, T313V manufactured by Toshiba (corresponding to the base material hardness P30) was used as a thread cutting chaser, and the cutting edge corner portion of the first cutting blade portion was chamfered to have a predetermined radius of curvature.

Here, the evaluation results shown in Table 1 show that when the steel pipe to be cut is made of carbon steel, 70 (± 10%) of the steel pipes to be cut can be cut without causing any chipping or the like of the blade portion. Was marked with “◯”, “◎” when more than that could be cut, and “x” when less than that could be cut. Similarly, when the steel pipe to be cut is made of 13Cr steel, “○” indicates that 50 (± 10%) of the steel pipes to be cut can be cut without causing any chipping of the blade portion. When it was possible to cut a larger number, “◎”, and when only a smaller number could be cut, “x”. In addition, when the steel pipe to be cut is made of high alloy, “30” is given when 30 (± 10%) of the steel pipes to be cut can be cut without causing any chipping of the blade portion, and so on. When the number was able to be cut, “◎”, and when only a smaller number could be cut, “×”.

  As shown in Table 1, when cutting was performed under the conditions (Examples 1 to 8) satisfying the above-described formula (1), a sufficient life could be obtained. In particular, when cutting was performed under the conditions (Examples 1 to 6) that also satisfy the above-described expression (2), the conditions that satisfied the expression (1) but did not satisfy the expression (2) (Examples 7 and 8). A much more sufficient life (number of pieces that can be cut) could be obtained compared with the case of cutting with the above method. On the other hand, when cutting was performed under conditions that did not satisfy Formula (1) (Comparative Examples 1 and 2), chipping of the blade portion occurred with a small number of cuttings.

FIG. 1 is a schematic cross-sectional view showing a state where a thread cutting method according to an embodiment of the present invention is applied. FIG. 2 is a graph showing a result obtained by approximating the actual value of the average cutting area of each blade portion constituting the chaser by a regression equation calculated on the right side of the equation (1).

Explanation of symbols

CH ... Chether C1, C2 ... Blade P ... Steel pipe

Claims (2)

A method of threading a steel pipe using a chaser provided with a plurality of blades for cutting a screw,
The average cutting area of the blade portion is S (mm ² ), the width of the blade portion for finishing cutting is B (mm), the height of the blade portion for finishing cutting is H (mm), the cutting speed is V (m / min), A steel pipe thread cutting method characterized by cutting under conditions that satisfy the following formula (1) when the Cr content of the steel pipe to be cut is C (%).
S ≦ 5.68 × 10 ⁻¹ × B-6.76 × 10 ⁻² × H−1.12 × 10 ⁻⁵ × V ² −1.68 × 10 ⁻² × C-5.82 × 10 ⁻¹ ... (1) Among the plurality of blade portions provided in the chaser, when the curvature radius of the cutting edge corner portion of the first cutting blade portion viewed from the cutting direction is r (mm), the chaser satisfies the following formula (2). The steel pipe thread cutting method according to claim 1, wherein cutting is performed.
0.2 × B ≦ r ≦ 0.5 × B (2)

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